1. Field of the Invention
The present invention relates to gas-powered water heaters, particularly those for residential use, and devices to shield the heating and pilot light burners from flammable vapors in the immediate area while improving air flow to the burners.
2. Description of the Relevant Art
Fuel-fired storage-type domestic water heaters are commonly used, and are popular because of their efficiency, economy and responsiveness compared with electric water heaters. Such devices are well known, and are described broadly in numerous publications, e.g. the background sections of U.S. Pat. Nos. 5,085,205 and 5,797,355. Such heaters can be used outdoors or indoors, but are typically used indoors, where the storage or spillage of flammable liquids or the like may give rise to hazards due to the close proximity of the heater pilot light, and heating burners and combustion air inlets to the floor, where such spillage typically takes place. These hazards are discussed at length in the patents just cited.
Various heater designs have been created, patented or produced to reduce or eliminate the hazards of the ignition of flammable vapors by the burners of the heater. Combustion air can be provided by direct venting from outside the heater space, which generally requires powered fans or other intake devices, takes considerable space for venting and is costly. Additionally, when a heater is provided air by venting from a distance, special control mechanisms must be provided to confirm the flow of air and the burning of the pilot light before the gas valve opens. Such controls are costly and prone to disrepair. Sealed combustion devices generally operate in a similar manner to vented systems, and have many of the same problems. Elevating a water heater on a stand at least 18 inches above the floor (in accordance with many building codes) is a simple mitigating method which is effective in many cases, but cannot prevent ignitions in all foreseeable circumstances.
Combustion air can be obtained from the immediate area of the heater via cylindrical enclosures which elevate the air intake further (resembling a xe2x80x9cbucketxe2x80x9d), or from elevated intake devices, collectively and informally referred to as xe2x80x9csnorkels,xe2x80x9d but these are not much more effective and may also increase the cost of the basic water heater installation. Various types of flame arrestor devices have been used with gas-fired water heaters to prevent the ignition of flammable vapors in the vicinity of an operating heater, but such devices impose a cost for the safety features offered, and also a burden of maintenance since they may tend to become clogged with debris or otherwise malfunction.
Hall""s U.S. Pat. No. 5,085,205 discloses an elevated air intake using an open xe2x80x9cbucketxe2x80x9d or cylindrical enclosure. Harrigill""s U.S. Pat. No. 6,035,812 discloses a heater with a bottom air intake and flame arrestor system. Bourke""s U.S. Pat. No. 5,797,355 discloses several systems having flame arrestors and elevated (xe2x80x9csnorkelxe2x80x9d) air intakes. Heaters related to the latter patent are sold under the trademarks xe2x80x9cFLAME GUARDxe2x80x9d and xe2x80x9cFLAME LOCKxe2x80x9d.
U.S. Pat. Nos. 5,575,273; 5,533,495 and 6,058,892 are related and relevant art, disclosing representative air intake systems. Moore""s ""273 and ""495 patents are closely related, and disclose xe2x80x9cbalanced fluexe2x80x9d heaters for outdoor use, having air intake openings on the upper vertical face of the outer jacket and ducts to carry the air down to the burner below the tank. FIG. 3 of the ""495 patent shows an essentially annular air duct, interrupted only by blocks 74, while the ""273 patent (FIGS. 1 and 2) shows a more conventional vertical air duct limited to only a portion of the annular space between tank and jacket. U.S. Pat. No. 6,058,892 discloses exterior tubular air intakes with open tops.
U.S. Pat. No. 5,765,547 discloses (see FIGS. 5/6, col. 8/9) a water heater with an exterior sealed shell forming a partial annular air passage for combustion air, with air entering side-opening vents at elevated positions above the middle of the heater.
U.S. Pat. No. 5,848,586 discloses a water heater with a xe2x80x9cfire safety collar,xe2x80x9d including two concentric air baffles which shield the burner from flammable vapors and form an annular air duct for combustion air intake from a position above the base of the unit.
U.S. Pat. No. 5,361,729 discloses (in FIGS. 17-23 and related text) a gas water heater with a partitioned flue including rectangular air intakes. Columns 7/8 and FIG. 17 describe the use of tapered exhaust ducts to affect heat transfer.
U.S. Pat. No. 3,091,223 discloses a sealed vent water heater with a xe2x80x9csnorkelxe2x80x9d air intake.
U.S. Pat. No. 5,365,887 discloses an on-demand water heater and heat exchanger. FIGS. 1 and 6 show air entering the outer shell through open vents and passing downward through an apparently annular air intake to provide combustion air to a burner shielded from the exterior environment.
Bowman""s U.S. Pat. Nos. 6,074,200 and 6,139,311 (the latter a CIP of the first), assigned to Gas Research Institute, disclose burner systems with the pilot light exposed to the ambient atmosphere to monitor the presence of flammable vapors and shut down the burners when necessary for safety purposes.
A large collection of patents was found which were all assigned to the same Australian company. Several of these patents are related as divisionals, continuations or continuations-in-part of older applications. Significant patents and disclosures include:
U.S. Pat. No. 6,138,613 discloses a xe2x80x9csnorkelxe2x80x9d intake using vertical-louvered air inlets. (Cont. Of U.S. Pat. No. 5,797,355)
U.S. Pat. No. 6,142,106 discloses air inlets with flame arrestors, designed to admit both air and extraneous vapors to the combustion chamber. U.S. Pat. No. 6,085,699, a CIP of U.S. Pat. No. 5,797,355, discloses similar air vents.
U.S. Pat. No. 5,797,355 discloses a gas water heater with a side-mounted xe2x80x9csnorkelxe2x80x9d intake having louvered air inlets.
U.S. Pat. No. 6,003,477 discloses snorkel intakes, both open and closed, and including flame traps. (CIP/CIP/CIP of U.S. Pat. No. 5,797,355)
U.S. Pub. No. 2001/0010209 (continuation of division of U.S. Pat. No. 5,797,355) also discloses vertical snorkel intakes with elevated louvered inlets.
U.S. Pat. No. 6,196,164, a division of U.S. Pat. No. 6,003,477, discloses vertical snorkel intakes with louvered inlets or open tops, and flame traps for use therein.
U.S. Pub. No. 2001/001529 (a continuation of division of U.S. Pat. No. 6,138,613, a continuation of U.S. Pat. No. 5,797,355) also discloses vertical snorkel intakes with elevated louvered air inlets.
U.S. Pub. No. 2001/0009144 (continuation of U.S. Pat. No. 6,196,164) discloses vertical snorkel intakes with elevated louvered air inlets and flame traps.
U.S. Pat. No. 6,293,230 discloses gas water heaters with air inlets/flame traps to admit both air and extraneous fumes to the combustion chamber.
U.S. Pat. No. 6,295,951 (CIP/CIP of U.S. Pat. No. 5,797,355) discloses side-mounted snorkel intakes with flame traps.
Clearly, despite the efforts of many designers and manufacturers in the mature industry serving the residential water heater market, there remains the need for simple, economical yet effective means of providing an efficient and responsive water heater which is reasonably safe against the hazards of flammable vapors in the vicinity. Homeowners and other purchasers are sensitive to prices for such appliances, and will normally pay only a limited premium for safe heaters, while perhaps honoring fire safety precautions more in the breach than the observance.
It is an object of the present invention to provide apparatus which renders conventional fuel-fired water heaters safe in the presence of flammable vapors or other materials. Another object of the invention is to provide a smooth flow of combustion air from the vicinity of the heater to the combustion chamber of the heater without disruption from drafts, wind or other air disturbances, pressure fluctuations or the like. Still another object of the invention is to prevent any reversals of direction of the combustion air supply or exhaust fumes upon startup of the heater, exterior drafts or other unusual conditions. Yet another object of the invention is to prevent the entry of foreign particulate matter into the combustion air intake system. A further object of the invention is to improve the insulation of the water storage tank and/or to increase the temperature of the incoming combustion air to improve the combustion process. Still another object of the invention is to elevate the heater tank, combustion chamber intakes and burners sufficiently within the heater apparatus to optimize the flow of air (i.e., make it smooth and steady) from the intake system to the combustion chamber and reduce the chances of reversals of flow of combustion gases. A fundamental object of the present invention is to achieve at least a portion of the above objects without significant increases in material, manufacturing or installation costs. To be effective in reaching many consumers, even the best safety devices must be price-competitive and be simple to install, operate and repair or replace. Another significant object of the invention is to provide improved performance while meeting all applicable electrical safety and emissions standards and the like.
Some of the advantages provided by the apparatus of the invention include:
Significant reductions in the potential ignition of vapors from a flammable liquid spill;
Prevention of potential reversals of direction of combustion air supply and/or exhaust fumes upon burner start-up or in the presence of unusual external winds;
Additional insulation afforded by the exterior cylindrical shell and the air enclosed within, reducing heat losses from the stored hot water via convection, conduction and radiation mechanisms;
Heating of combustion air above ambient temperature as it passes through the annular air passage surrounding the tank, which improves combustion efficiency;
Essentially invulnerable to clogging by airborne debris which might clog flame-arrestor devices; and
Minimal added material and manufacturing costs compared with conventional storage heaters.
These and other objects and advantages are attained by the apparatus and method of the present invention, comprising means for positioning a conventional gas-fired water heater within a shell having a solid base and an open top and configured to fit over the water heater to provide an annular passage between shell and heater which allows air to flow smoothly from an intake formed by a detachable cover atop the shell to the combustion chamber below. The heater is positioned and fastened within the shell so that the combustion chamber is located a vertical distance above the base of the shell effective to smooth (i.e., make non-turbulent) the flow of combustion air from the air intake to the combustion chamber without allowing reversals of flow of either the combustion air or combustion gases.
In a form which can be adapted to fit almost any conventional gas-fired water heater, the invention comprises a cylindrical shell adapted to enclose the heater, fitted with a solid base and sealed substantially air-tight except for an open top, the top being fitted with a detachable cover whose edge is displaced downward sufficiently to form a lip to deflect lateral air flow from outside the shell and direct air into the annular space formed between the tank and shell from below the cover and via an air intake. The shell preferably comprises an access door which can be removably closed air-tight and may contain a transparent portion for burner observation. The base of the shell can include support means to elevate the bottom of the shell above the floor where the unit is installed.
A method of installing a gas-fired water heater in the shell described above comprises steps of:
a) selecting the diameters of the heater and shell to establish an annular combustion air passage between the two which allows unrestricted air flow to the combustion chamber below;
b) adding a skirt extension with a solid bottom to the bottom of the heater, the skirt extension sealing the bottom of the heater except for a plurality of air intake holes in the extension bottom; then,
c) inserting the heater into the shell and securing it in a centered position an effective distance above the base of the shell with securing means; and
d) emplacing the cover of the shell atop the shell and heater to shield the annular passage from above, prevent lateral airflow into the passage and direct combustion air into the passage from below the cover.
In installing the shell on an existing heater, the heater with its skirt extension is positioned within the shell to emplace the main burner(s) of the heater an effective distance above the base of the shell to optimize air flow (i.e., make smooth and steady) to the burner(s) and prevent reversals of flow of either intake air or combustion gases. By installing a conventional gas-fired water heater with skirt extension in such a shell of the invention, an improved water heater of the invention is provided.
Further in accordance with the invention, an improved gas-tired storage water heater can be produced, comprising a storage tank fitted with a cylindrical shield, the shield having a solid base and being sealed substantially air-tight except at the top. The shield surrounds the tank so as to define an annular air passage between the outer surface of the heater and the inner surface of the shield, the width of the passage being selected to provide a smooth, unrestricted flow of combustion air to the burner(s) of the heater. The heater is elevated a sufficient distance above the base of the shell to smooth the flow of combustion air from the annular passage into the combustion chamber of the heater, and a cover with a downward-displaced edge forming a lip is emplaced atop the shell and heater to shield the annular passage from the top and sides, thus directing combustion air into the annular passage from below the cover with a substantial change of direction in the process.
Further refinements to this manufactured embodiment of the invention include a skirt extension which extends from the bottom of the heater to enclose the combustion chamber and burner(s) of the heater in an airtight manner except for a plurality of air inlets in the bottom of the skirt extension. These air inlets are provided in sufficient size and number and suitable arrangement in the skirt extension bottom, and the heater with extension installed is emplaced to position the burner(s) of the heater a sufficient distance above the base of the shell to optimize the flow of combustion air to the burner(s) and prevent reversals of flow of intake combustion air or combustion gases. Suitable support and attachment means are provided to position the heater within the shell to form a suitable annular passage and to elevate the heater (and skirt extension, when installed) an effective distance above the base of the shell. Support means can be fitted to the bottom of the shell to elevate the heater-containing shell above the floor where installed. At least one sealingly closable access door can be provided in the shell for access to components of the heater, optionally including a transparent portion for burner operation. The heater can include a layer of insulation surrounding at least the sides of the tank, which must be considered in selecting or constructing a shell of a particular diameter.